The Early and Periodic Screening, Diagnosis, and Treatment (EPSDT) program under Medicaid was created by the Social Security Amendments of 1967 to detect and treat correctable conditions in Medicaid-eligible children and to rescreen those children periodically to ensure continued good health. EPSDT represents a significant extension of health care benefits to children as a matter of statutory right. Its evolution from a statement of law to an operational program has been a prolonged and difficult process influenced in part by many organizations interested in health care and children. This study aims to describe that influence and to discover what patterned relationships there are, if any, among organizational characteristics, the interorganizational network involved and organizational activity. A developmental research design employing case study methods is proposed which features a concept of policy implementation termed "policy activation". This concept emphasizes the view that implementation takes place in an interorganizational context characterized by competition for control of the way in which resources and influence are distributed in pursuit of a given nominal policy (e.g., EPSDT). The findings of this study are expected to be of use to child advocacy and other consumer organizations, federal, state, and local health planning and service delivery organizations, and to health policy researchers.